Wild Weekend Ahead

A large and impactful low pressure system is set to develop in the Tasman Sea during the day on Friday, and it will be making its way towards the west coast of the North Island by early Saturday morning. As this system approaches, heavy rain and severe gales are likely to have a significant impact on the central and southern areas of the North Island, with effects spreading across both the east and west coasts. Meanwhile, for the South Island, heavy rainfall is expected to affect the northern and western regions, with total accumulations potentially reaching significant levels. Additionally, there is a forecasted potential for snow in the Alpine regions, which could extend to lower elevations in the far southern parts of the island. It is vital to note that as we expand on the evolving situations below, all forecasts are subject to change, right up to and including during both weather events; however, there has been a substantial increase in confidence regarding these predictions based on the latest model forecasting data.

Saturday

Sunday

Heavy Rain

Over the last seven days, the model data has produced various positions regarding where the low pressure system may cross over the country. However, since Tuesday, the trends have become more solidified and have now clearly identified the specific location where it is anticipated to cross over New Zealand. This is a vital piece of information, as it will greatly assist us in accurately predicting which areas will be most affected by the forthcoming severe weather conditions.

• Rain is expected to develop across the North Island during the afternoon on Saturday, with the intensity of the rainfall increasing significantly for Taranaki in the evening hours. Heavy downpours are particularly likely, especially in the areas surrounding the summit of Mt Taranaki, which could experience the most significant rainfall. In addition, rain will also make its way into the northern part of the South Island, where a period of heavy rain is anticipated for the Tasman region overnight as the low pressure system makes its way across central New Zealand.

• On Sunday, the heavy rain will not only persist but also intensify as additional moisture from the Tasman Sea arrives. These significant downpours are expected to continue for various parts of the Central North Island, but they will also considerably affect the Kapiti Coast, Tararua Ranges, Central High Country, and Eastern Bay of Plenty, as well as the Buller District.

• Remaining rain or occasional showers are expected to ease by late morning on Monday, with conditions becoming increasingly clearer as the day progresses, leading to a more settled atmosphere by the evening hours.

• Rainfall totals over the weekend for the areas identified above are currently forecasted to be in the region of approximately 80-120mm, with the mountains and ranges potentially receiving significantly more precipitation due to the topography.

• The areas mentioned above have been identified as those at the highest risk for significant rainfall totals. In addition to these regions, other areas including Waikato south of Hamilton, parts of Bay of Plenty west of Whakatane, as well as the Manawatu, Wellington, Tasman, and Westland, are also at a higher likelihood of experiencing significant accumulations if rainfall increases overall. We are continuously and closely monitoring the evolving situation and advise all residents in these affected areas to remain vigilant and keep checking our Significant Weather Outlook, which can be conveniently found on our homepage for the latest updates and information.

Severe Gales

Strong winds are also incorporated with this dynamic low pressure system, as northwesterly winds are expected to arrive alongside the heavy rain associated with this weather pattern. At this stage, we have forecasted that wind gusts could reach severe gale strength for a period of time throughout the duration of this event, particularly around the elevated areas of the Hawke’s Bay ranges and Gisborne. Additionally, the Wairarapa region, including Wellington and the Cook Strait area, could also experience severe gales gusting 80-120 km/h during this event . In exposed locations and sheltered valleys, wind gusts are projected to reach higher speeds which we are closely monitoring.

Snow Risk

We are keeping a close eye on potential snow risks, both associated with this incoming weather feature and a very cold southwesterly flow following. There is still considerable uncertainty, so expect things to change going forward and to keep a close eye on our weather outlooks and our in depth analysis closer to the time… So, what are we expecting?

• There is a possibility, albeit slight, for a period of warm advection snowfall in Canterbury and Marlborough on Saturday night and early Sunday morning - this risk is dependant on whether enough cold air can make it in time to undercut the rain band feeding in from the northwest. Snow could be possible to 400-500 metres. There is only slight confidence in this occurring, so keep an eye on updates from us.

• During Sunday we are expecting the initial main cold change to move north across most of the South Island with the coldest air (during Sunday) moving in during the afternoon and evening. Showers are likely going to be few and far between for Southland and Otago but snow is possible to 300-400m, especially from evening but with minimal accumulation. Into Canterbury, expect the odd shower becoming more frequent late afternoon or evening and snow is possible to 500m from evening - from 4pm-11.59pm Sunday 2-4cm possible above 600m, and 4-7cm above 800m.

• The coldest surge of air is during Monday - but like Saturday night our confidence is low so keep a close eye for updates from us.. Showers could become more frequent for Southland and Otago in the morning, with snow possible to low levels. At this stage it is looking like Canterbury will miss the most in this very SW flow, with early morning snow showers above 500m retreating to North Canterbury and Marlborough before becoming quite isolated and returning elsewhere but may lower a little on earlier levels heading into the afternoon and evening. The best chance for snow on Monday in Canterbury will likely be above 500m on Banks Peninsula.

There is a lot going on snow-wise, with a lot to monitor but we will keep you informed on the latest - see our Significant Weather Outlook and In-Depth Analysis.